Variable density window



L :earch Room sept. 1s, 1941. E H LAND" 2,255,933

VARIABLE DENS ITY WINDOW f" Filed Dec. l2, 1940 L `,yl-1G. l

FIG. 2

30 as L Sept. 16, 1941 Search Room VARIABLE DENSITY WINDOW Edwin H.Land, Cambridge, Mass., assignor to Polaroid Corporation, Dover, Del., acorporation of Delaware Application December 12, 1940, Serial No.369,763

(Cl. Sli-65) 9 Claims.

This invention relates to variable density windows.

An object of the invention is to provide a variable density windowcomprising a plurality of overlying, light-polarizing elements havingmeans associated therewith for controlling at will the amount of lighttransmitted thereby.

Another object is to provide such Ia window wherein the light-polarizingelements are bonded together in laminated form and wherein the densityof the window as a whole is varied by the application of suitable forcedirectly to said lamination.

A further object is to provide such a window wherein the bonding meansbetween the polarizing elements comprises a rubbery elastic, transparentcement which is substantially isotropic in its normal condition butwhich may be converted to act as a half wave retardation device upon theapplication of predetermined stress.

A still further object is to provide such a laminated window wherein thedensity of the window as a whole is varied by moving one polarizer withrespect to the other and thereby exerting a shearing force on the cementlayer suflicient to cause it to function as a half wave retardationdevice.

Other objects and advantages will in part appear and in part be pointedout in the course of the following description of an embodiment of theinvention, which is given as a non-limiting example, in connection withthe accompanying drawing, in which:

Figure 1 is a sectional view showing a variable density window embodyinga form of the invention;

Figure 2 is an elevation of the window shown in Fig. 1; and

Figure 3 is a partial, sectional view showing a modification of a partof the window shown in Fig. 1.

In its simplest embodiment, the variable density window of the presentinvention comprises a pair of parallel, overlying polarizing surfaceswhich are preferably positioned with their transmission axes eitherrelatively parallel or relatively perpendicular. Said polarizers arebonded together by means of a transparent, rubbery cement which isisotropic when not under stress but is capable of functioning as a halfwave retardation element when subjected to a shearing force. Means areprovided for moving one of said polarizers in the plane thereof withrespect to the other and thus for exerting a shearing force on saidcement layer.

The degree of motion of said polarzer may be carefully controlled, andthus the light passing through each polarizer may have its vibrationcharacteristics altered at will so that it may be either transmitted orabsorbed by the other said polarizing element.

Referring to Figs. 1 and 2, element I Il represents a channeled windowframe formed in any conventional manner and providing a window apertureof substantial area. Mounted in frame I0, as by means of element I2, isa laminated window element comprising a pair of layers I4 and I6 ofpolarizing material, bonded together by means of a layer of cement I5and covered by protecting plates I8, 20 of glass or other rigid,transparent plastic. The other side of frame I0 may be provided with anysuitable ange means 22 of conventional design.

Polarizing layers I4 and I6 are of substantially uniform polarizingproperties and may conveniently be made from one of the polarizingsheets or lms sold under the trade name Polaroid". They may bepositioned with their respective transmission axes at any desired angleto each other, but preferably said axes will be relatively perpendicularand at angles of 45 to the vertical, as indicated-in Fig. 2, whereinarrows 24 and 25 represent the transmission axes of polarizers I4 and I6respectively.

Cement layer I5 may comprise virtually any transparent, rubbery,adhesive material which will bond to polarizing layers I4 and I6 or toglass and other relatively hard plastics. Among satisfactory materialsfor this purpose there may be mentioned as illustrative examples vinylacetate plasticized with dibutyl phthalate, and incomplete vinylbutyral, known as Vinylite X, plasticized with any suitable medium suchas dibutyl phthalate. Layer I5 may be of any desired thickness, thecontrolling factor being that the thicker the layer, the greater theamount of shear necessary to cause it to function as a half waveretardation element. It will be understood, however, that layer I5 hasbeen shown in Fig. l in highly exaggerated and diagrammatic form.

As is shown in Fig. l, there are provided within frame I0 suitable meansfor exerting force on one of the polarizing elements in such manner asto exert shear on layer I5. Glass cover plate 20 is provided along itsupper edge with a channeled rim 26 which is slidable between spacerelements 28 and bears against one or more compression springs 30. Alongits lower edge, plate 20 is provided with a similar rim 32 which isslidable between spacer elements 34 and is in contact with a suitablecam 35 or other similar device. Cam

35 is mounted on shaft 36 and provided with suitable means forcontrolling its rotation, said means comprising gear 38 meshing withworm 42, controlled by crank or knob 40 journaled in frame l0. It willof course be understood, however, that this cam mechanism is merelyillustrative of the many similar means for exerting force on plate 20 inaccordance with the practice of the invention.

It is believed that the operation of the above described window will nowbe apparent. Layer I5 is preferably of such characteristics that it isoptically isotropic when the device is in the position shown in Fig. 1,that is to say, when cam 35 is exerting the least pressure. Inasmuch,therefore, as the operation of layer I5 may be disregarded, and inasmuchas polarizers I4 and I6 are positioned with their transmission axesrelatively perpendicular, it will be seen that this is the position ofmaximum extinction for the window. As cam 35 is rotated, plate 20 iscaused to move upward, and since plate I8 is rigidly held, this exerts ashearing force on cement layer I5. This force gradually causes themolecules or micells in the cement to become oriented and so causeslayer I5 to become Vbirefringent. The 'birefringence increases with theorientation, and the layer therefore exerts a gradually increasingrelative retardation with respect to one component of the polarizedlight transmitted by, for example, polarizer I4. As the relativeretardation increases, more and more light has its polarizationcharacteristics altered to a condition wherein it is transmitted bypolarizer 20. When the stress reaches the degree whereat layer I5becomes a half wave retardation plate, all of the light transmitted bypolarizer I4 will have its vibration direction rotated through 90 andthus will be transmitted by polarizer I6. It follows that the positionof maximum transmission is that wherein layer I5 is subjected to such adegree of shear that it functions as a half wave plate.

The positions of the polarizing elements with respect to their axes maybe changed to a considerable extent. However, the illustrated positionis preferred. It will be understood also that in order to obtain themaximum density variation in this arrangement, the direction of theforce applied to layer I5 and plate 20 should be at 45 to the axes ofthe two polarizers, as in the arrangement shown in Figs. 1 and 2. ItWill of course be obvious that the polarizers may be positioned withtheir axes parallel, and in this case also the force should preferablybe at an angle of 45 to said axes. Various other relative positions ofthe polarizers and direction of force may also be used, but thepositions above are preferred.

Fig. 3 shows a modication of the invention wherein the relativepositions of the various layers in the lamination ar changed. Layer 45in Fig. 3 corresponds to layer I5 in Fig. 1, and layers 44 and 46represent polarizing layers corresponding to layers I4 and I6 in Fig. 1.Layers 48 and 50 represent sheets or plates of glass or other suitablyrigid, transparent plastic, and layers 52 and 54 represent additionalcover plates for the polarizing layers and may comprise thin sheets ofglass or other plastic or a protective coating of a suitable substancesuch as a lacquer. It will be understood that the unit shown in Fig. 3may be substituted for the corresponding unit in Fig. 1, and that theoperation will be substantially the same as that described in connectionwith Fig. 1. Many other modifications of the aboye construction willalso doubtless be apparent and are construed as within the scope of theinvention and of the claims herein.

The plastic employed as the cement layer, I5

in Fig. 1 and 45 in Fig. 3, should be a plastic, as has been pointedout, which is rubbery-elastic, i. e., which possesses the property ofreturning to its initial condition after the stress to which it has beensubjected has been removed, and it should show substantially no coldflow when subjected to the stress rendering it birefringent.Furthermore, it should preferably have a high positive or negativestress optical coeiiicient. The materials already mentioned for use inthe device possess these characteristics to a satisfactory degree.

It should be understood furthermore that while a preferred embodiment ofthe invention constitutes the provision of means for subjecting thecement layer to a stress which results in it functioning as a half-waveretardation device, such a preferred condition is not necessary in thepractice of the invention. It may for example be desirable only topermit a small percentage of light to be transmitted or it may beunnecessary for the device to function to completely block incidentlight in the position of maximum extinction. Any of these modificationsare to be deemed to fall within the scope of the invention.

It may be said of the device of the present invention that it comprisesa plurality of lightpolarizing elements bonded together either directlyor by a bond connecting their supporting plates by means of a materialsuch that the transmission of the entire device for light incident oneither surface as a function of the stress applied to the bondingmaterial through the relative motion of one of the light-polarizingelements with respect to the other in a direction substantially parallelto the plane of the other said polarizing element.

Since certain changes may be made in the above construction, anddifferent embodiments of the invention could be made without departingfrom the scope thereof, it is intended that all matter contained in theabove description or shown in the-accompanying drawing shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. A variable density window comprising, in combination, means providinga plurality of substantially superimposed, relatively parallel,lightpolarizing elements, a layer of transparent, rubbery cement betweensaid polarizing elements, said cement being adapted under apredetermined stress to function as a half wave retardation element, andmeans for moving one of said polarizing elements with respect to theother and simultaneously exerting a shearing force on said cement layersufficient to cause it to function substantially as a half waveretardation device.

2. A variable density window comprising, in combination, a plurality oflight-polarizing elements, said elements being bonded together insubstantially parallel and superimposed relation, said bonding meanscomprising a. transparent,

B8. OPTICS rubbery cement, said cement being capable under predeterminedstress of functioning as a half wave retardation element, and means formoving one of said polarizing elements in the plane thereof with respectto the other said element and thereby exerting a shearing force on saidcement layer sufficient to cause it to function substantially as apredetermined wave retardation device.

3. A variable density window comprising, in combination, a plurality oflight-polarizing elements, said elements being bonded together insubstantially parallel, superimposed relation with their respectivetransmission axes at a predetermined angular relation to each other,said bonding means comprising a transparent, rubbery cement, said cementbeing capable under a predetermined stress of functioning as a half waveretardation element, and means for moving one of said polarizingelements in the plane thereof with respect to the other said element,thereby exerting a shearing force on said cement layer suilicient tocause it to function as a predetermined Wave retardation device, saidmotion being in a direction at equal angles to the transmission axes ofsaid polarizing elements.

4. A variable density Window comprising, in combination, a plurality oflight-polarizing elements, said elements being bonded together insubstantially parallel, superimposed relation with their respectivetransmission axes relatively perpendicular, said bonding meanscomprising a transparent, rubbery cement, said cement being capableunder a predetermined stress of functioning as a half Wave retardationelement, and means for moving one of said polarizing elements in theplane thereof with respect to the other said element, thereby exerting ashearing force on said cement layer suiiicient to cause it to functionas a half Wave retardation element, said motion being in a direction atangles of 45 to the transmission axes of said polarizing elements.

5. A variable density window comprising, in combination, a plurality oflight-polarizing elements, said elements being bonded together insubstantially parallel, superimposed relation with their respectivetransmission axes relatively parallel, said bonding means comprising atransparent, rubbery cement, said cement being capable under apredetermined stress of functioning as a half wave retardation element,and means for moving one of said polarizing elements in the planethereof with respect to the other said element, thereby exerting ashearing force on said cement layer sufficient to cause it to functionas a half wave retardation element, said motion being in a direction atangles of 45 to the transmission axes of said polarizing elements.

6. A variable density window comprising, in combination, frame meansproviding a window aperture of substantial area, a plurality ofsubstantially parallel glass plates positioned within said frame andoverlying said aperture, means providing a plurality of light-polarizingsurfaces `Search Roen-i of substantially the same area as said aperture,one of said polarizing surfaces being associated with each of said glassplates, means comprising a layer of transparent, rubbery cement bondingsaid plates together, said cement being adapted upon the application ofa predetermined shearing force to function as a half wave retardationdevice, means for positioning one of said glass plates fixedly withinsaid frame, and means for moving the other of said glass plates in theplane thereof and thereby exerting a predetermined shearing force uponsaid cement layer to vary the amount of light transmitted by saidwindow.

7. A variable density Window comprising, in combination, means providinga plurality of substantially superimposed, relatively parallel,lightpolarizing elements, a layer of transparent, rubbery-elastic cementshowing substantially no cold oW between said polarizing elements, andmeans for moving one of said polarizing elements with respect to theother and simultaneously exerting a shearing force on said cement layer,the transmission of said window for light incident normally on eithersurface thereof being a function of the force applied to said cementlayer.

8. A variable density window comprising, in combination, a plurality oflight-polarizing elements, said elements being bonded together insubstantially parallel, superimposed relation with their respectivetransmission axes at a predetermined angular relation to each other,said bonding means comprising a transparent, rubberyelastic cement, saidcement having a high stress optical coefficient and showingsubstantially no cold iiow, and means for moving one of said polarizingelements in the plane thereof with respect to the other said element,thereby exerting a shearing force on said cement layer suiiicient tocause it to function as a wave retardation device, said motion being ina direction at equal angles to the transmission axes of said polarizingelements.

9. A Variable density window comprising, in combination, frame meansproviding a window aperture of substantial area, a plurality ofsubstantially parallel glass plates positioned within said frame andoverlying said aperture, means providing a plurality of light-polarizingsurfaces of substantially the same area as said aperture, one of saidpolarizing surfaces being associated with each of said glass plates,means comprising a layer of transparent, rubbery cement bonding saidplates together, said cement showing substantially no cold flow whensubjected to a stress and having a high stress optical coefcient, meansfor positioning one of said glass plates flxedly within said frame, andmeans for moving the vother of said glass plates in the plane thereofand thereby exerting a predetermined shearing force upon said cementlayer to vary the amount of light transmitted by said window, thetransmission of light by said window being a function of the shearingforce applied to said cement.

EDWIN H. LAND.

